In the past, when an accident such as an earth fault or a short circuit occurs in a power distribution system of a power system, a monitoring control system performs a switching control of switches such that an accident section separated by two switches around an accident spot is instantly isolated, and a power is distributed to the other sections. An example of a conventional monitoring control system, which monitors and controls a power distribution system, will be described with reference to FIG. 15. FIG. 15 is a block diagram illustrating a configuration of a conventional monitoring control system installed in a power distribution system.
In FIG. 15, the power distribution system 900 is designed to distribute a power from a transformer 902 provided within a distribution substation 901 by using a distribution line. In order to limit effects as much as possible when an accident such as an earth fault or a short circuit occurs in the distribution line, the power distribution system 900 includes circuit breakers (CBs) 911 and 916 for disconnecting the distribution system from the transformer 902, and a plurality of switches 912 to 915 and 917 to 921 in the middle of the distribution line. Also, the power distribution system 900 includes a monitoring control system 930 for monitoring an occurrence of an accident and appropriately processing this. The monitoring control system 930 includes a master station (center device) 903 and also includes slave stations 932 to 935 and 937 to 941 at the switches 912 to 915 and 917 to 921, respectively. The slave stations 932 to 935 and 937 to 941 are directly connected to the master station 903 via a predetermined communication line, or are connected to the master station 903 through other slave stations.
In the conventional example illustrated in FIG. 15, distribution lines of two systems are connected from the transformer 902 through the CBs 911 and 916, and four switches 912 to 915 and four switches 917 to 920 are disposed therein, respectively. In addition, two distribution systems can be connected together by the switch 921. Also, the slave stations 932 to 935 and 937 to 941, which are respectively provided at the switches 912 to 915 and 917 to 921, are connected to the master station 903 by using a predetermined communication line in the same connection relationship as the switches 912 to 915 and 917 to 921. In the conventional monitoring control system 930, a power line or a metal cable has been used as the communication line. The configuration of the conventional monitoring control system is disclosed in, for example, Patent Literature 1.
In the power distribution system 900 described above, for example, when an earth fault accident occurs, an accident treatment method (hereinafter, referred to as a first accident treatment method) by the conventional monitoring control system 930 will be described below. In FIG. 15, when an earth fault occurs at a spot A, the CB 911 is interrupted and a power distribution to a more downstream side than the CB 911 is stopped. As a result, since the switches 912 to 915 receive no power, the switches 912 to 915 are non-voltage-opened.
When the master station 903 detects that the CB 911 has been interrupted and the switches 912 to 915 have been non-voltage-opened, the master station 903 first confirms that no earth fault current is generated by performing a closing control on the CB 911 so as to detect an accident section and resume a power distribution to sections other the accident section. After that, the master station 903 instructs the slave station 932 to perform a closing control on the switch 912. The slave station 932 performs the closing control on the switch 912 according to the instruction from the master station 903. However, since the switch 912 is not the accident section, the earth fault current is not generated and the CB 911 is not interrupted.
When the master station 903 confirms that the CB 911 is not interrupted even when the closing control is performed on the switch 912, the master station 903 also instructs the slave station 933 to perform a closing control on the switch 913. The slave station 933 performs the closing control on the switch 913 according to the instruction from the master station 903. At this time, since the earth fault current flows again through the accident spot A, the CB 911 is interrupted again. As a result, the switches 912 to 915 are non-voltage-opened again. Therefore, the master station 903 determines that the accident section is located between the switches 913 and 914. Then, the switches 913 and 914 of the accident section are locked.
After the closing control of the CB 911, the master station 903 instructs the slave station 932 to perform a closing control on the switch 912 so as to resume the power distribution to a more upstream side than the locked switch 913. When the slave station 932 performs the closing control on the switch 912 according to the instruction, the power distribution to the more upstream than the switch 913 is resumed. Also, after the locking of the switch 914, the master station 903 instructs the slave station 941 to perform the closing control on the switch 921. When the slave station 941 performs the closing control on the switch 921 according to the instruction, the power distribution is resumed in a section from the switch 921 to the switch 914. Therefore, the power distribution is resumed in all sections other than the accident section including the spot A.
The first accident treatment method by the conventional monitoring control system 930 has a problem in that in addition to the earth fault current in the occurrence of the accident, the earth fault current is generated again for the detection of the accident section, and power facilities are overloaded by the two earth fault currents. Also, since all the switches of the distribution system including the accident spot are temporarily opened, there is a problem that a power failure temporarily affects sections other than the accident section. Also, since the plurality of switches is opened by one accident, there is a problem that it takes time to restore it.
In this regard, there is known another accident treatment method (hereinafter, referred to as a second accident treatment method) that is configured to prevent an occurrence of a power failure except for accident occurrence. The second accident treatment method will be described below with reference to the power distribution system 900 and the monitoring control system 930 illustrated in FIG. 15. In the second accident treatment method, current waveforms or phases from the respective slave stations at the time of the accident are integrated into the master station 903. Therefore, the accident section is determined without causing the power failure again, and the corresponding section is isolated from the distribution system.
When the master station 903 determines that the accident occurred between the slave stations 933 and 934, the master station 903 instructs only the slave stations 933 and 934 to open the switches 913 and 914, respectively. When the slave stations 933 and 934 open the switches 913 and 914 according to the instruction, respectively, only the accident section is isolated from the distribution system. After the switch 914 is opened, the master station 903 instructs the slave station 941 to perform the closing control on the switch 921. When the slave station 941 closes the switch 921 according to the instruction, the power distribution is resumed in a section from the switch 921 to the switch 914. Therefore, the power distribution is resumed in all sections other than the accident section including the spot A.
In the second accident treatment method, the accident condition is continued until the switches 913 and 914 are opened and the accident section is isolated, and thus, the power facilities are overloaded. Therefore, the loads of the power facilities can be reduced by performing the above processing at a high speed (for example, several ten ms to several hundred ms).
However, in order to perform the second accident treatment method at a high speed, the master station needs to perform, at a high speed, the processing of inputting information about a direction of the accident section from each slave station, determining the accident section based on this, instructing two slave stations corresponding to the accident section to open the switches thereof according to the determination result, and instructing the closing control of the switches connected to other distribution system so as to resume the power distribution to the more downstream side than the accident section. As such, in the second accident treatment method, the load of the master station is increased and traffic is also significantly increased. Therefore, there is a need for a communication device and a communication system capable of coping with an increase in traffic.
A necessary control in the conventional monitoring control system 930 is only to open and close each switch, and is a low capacity that can be sufficiently covered by the communication line such as the metal line or the power line used in the conventional monitoring control system.
On the other hand, a lot of distributed power supplies, such as solar cells, wind power generation facilities, and fuel cells, have recently been connected to the distribution line. These distributed power supply facilities may cause a reverse power flow and cause a variation in the voltage of the distribution line. It is expected that the introduction of the distributed power supply will be more accelerated in the future, and it is essential to introduce a system that detects a voltage variation.
As the system capable of detecting the voltage variation, those using a switch with a sensor are beginning to be used. In the corresponding system, a voltage sensor is embedded into a switch, so that voltage data can be periodically acquired and can be transmitted to a substation.
As the introduction of the distributed power supply is in progress, capacity expansion is required because it is necessary to acquire high-frequency, high-accuracy voltage data and capacity shortage occurs in a communication network using the metal line or the power line used in the conventional distribution line communication. Also, such voltage data is data related to a stable supply of power, and high reliability is required even in a communication network that deals with transmission.
Therefore, in order to enable a stable high-capacity communication, it is preferable that the communication devices provided in the master station and the slave stations, and the communication system constructed by connecting them are made in an optical manner. Also, in the monitoring control system used in the distribution system, since it is necessary to arrange a plurality of slave stations in a distributed manner, it is preferable to reduce the load of the communication device installed in each slave station and easily perform the construction of the communication system or the addition of the slave stations. In a network of a TCP/IP standard, it is possible to add a routing function that can construct a communication network more flexibly than in the past. However, there has been a problem that the load of the routing function is heavy and the device increases in size. Also, in order to increase reliability, configurations capable of route redundancy are preferable. One of such configurations is a multi-hop communication system that uses TCP/IP and implements an L3 routing protocol in each communication device.
As one of multi-hop communication technologies, there is known a wireless communication technology of, for example, a ZigBee (registered trademark) standard, which connects a plurality of distributed nodes and performs a signal transmission with a target node via another node (relay processing). An Ad hoc On-demand Distance Vector (AODV), which is a route search algorithm adopted in the network of the ZigBee standard, is one of L3 routing protocols and can reduce the load of the routing processing and can miniaturize the communication device or reduce power consumption. Therefore, by introducing the ZigBee (registered trademark) standard adopting the AODV, which can easily achieve the miniaturization, load reduction, and low power consumption, into an optical communication capable of high-capacity communication, it is expected to realize a distribution-system communication device and a distribution-system communication system which are capable of performing large-capacity communication and reducing arithmetic processing.
Also, in the past, a distribution-line remote monitoring control communication system, to which IP is applied, has been put to practical use. As disclosed in, for example, Patent Literature 2, an IP communication is adopted in a communication network between master and slave stations of a distribution line, and thus, a route is duplexed. According to Patent Literature 2, a plurality of ports can be provided at one node by adopting optical SW-HUB, and high-capacity data communication can be realized at low cost by employing the IP typically used in high-capacity communications such as Internet. In addition to this, a function of maintaining a communication in an emergency is provided by duplexing a route for a distribution-line remote monitoring control communication system requiring high reliability.
Since high reliability is required in the distribution-line monitoring control system using the IP, it is preferable to perform a route redundancy and monitor whether each route is normal. In order to confirm whether a state of an optical path is normal, it is general to perform a management of physical layer information a transceiver has (for example, transmission/reception power). At this time, since it needs to be managed in conjunction with route switching information, it is necessary to recognize to which IP address each transceiver is linked. The communication device can perform matching by using an address correspondence table (ARP table in IPv4, neighbor cache in IPv6) matching IP address with MAC address, and can match ports with MAC addresses with reference to a table of an SW-HUB. Therefore, by matching information of two tables, information of the port and the IP address can be matched.